A 19th-century illustration of a tattooed body from the Skin exhibition at the Wellcome Collection. Photograph: Wellcome Images

Peter Johnston-Saint was an agent for Sir Henry Wellcome, the Wisconsin-born pharmaceutical magnate, who in Paris in 1929 made a peculiar purchase: a collection of more than 300 examples of tattooed skin, dating to 1850. The seller, a shadowy figure called La Valette, seems to have obtained the specimens via his work at Parisian military establishments and prisons; motifs ranged from flowers to female figures, patriotic slogans to inscriptions. Animals featured too: a cheetah and a pig on a bicycle.

Scholars of the period were increasingly interested in the practice of tattooing and anthropologists researched the complex social significance of tattoos in south-east Asia, Polynesia and of the Maori in New Zealand. Johnston-Saint's haul, while of a very difference provenance, was destined for Wellcome's collection of books, paintings and objects dealing with the historical development of medicine. Today, the tattooed skins form part of the Wellcome Collection, the museum established on the Euston Road in London, in 2007, and a handful of examples are star exhibits there in a new show called Skin.

This exhibition, according to its co-curator Javier Moscoso, from the Spanish National Research Council, "focuses on the historical transformation of both the scientific understanding and cultural significance of human skin, plotting it as beliefs, facts and popular mindsets have all evolved". What this means is a show divided into two main parts: Objects, which, among much else, looks at skin removal and flaying; and Marks, which examines skin as a living canvas.

But what of Johnston-Saint's haul of tattooed skins? Some of these, according to Gemma Angel, who is studying the Wellcome's collection for a Phd thesis, had been surgically removed; others would seem to have been hacked from corpses. Criminologists in the late Victorian period thought tattoos would be useful in identifying atavistic types; it is not known precisely why Wellcome wanted these examples in his collection.

Skin is at the Wellcome Collection, London NW1 (www.wellcomecollection.org), 10 June-26 September